Highest temperature in London on August 20?

Platform comparison

Market context

On 20 August 2026, the highest temperature recorded at London City Airport will determine which range this contract settles into. The market currently prices all temperature bands at 0% probability on Polygon, suggesting either extreme illiquidity or a technical issue with the USDC-denominated conditional tokens. Resolution hinges on the Daily Observations table from Weather Underground rather than headline figures, a distinction that matters when intraday spikes occur between official recording intervals.

London's August temperatures have historically clustered between 20–26°C, with extremes rare but documented. The summer of 2022 saw the UK's record high of 40.3°C, though London itself peaked at 37.8°C that July. August typically runs cooler than July; the past decade shows August highs in the capital averaging 23–24°C, with readings above 30°C occurring roughly once every three to four years. The 0% crowd probability suggests traders may be waiting for meteorological forecasts closer to the date before committing capital, or the market lacks sufficient depth to establish meaningful price discovery.

The UK Met Office publishes extended outlooks approximately two weeks ahead, with notable updates in early August 2026 providing the first reliable signals for temperature distribution. Atlantic weather patterns and jet stream positioning in mid-August will determine whether high-pressure systems deliver continental warmth or Atlantic systems bring cooler, wetter conditions. Traders should monitor these forecasts alongside any historical anomalies flagged by Weather Underground's station maintenance schedules, which could affect data quality at London City Airport.

Methodology

Methodologically we separate two layers: the live probability (Polymarket mid-price) and the platform attributes (fee, KYC, settlement currency, payment rails). That keeps the comparison honest — a single canonical probability across the row, with the venue-by-venue trade-offs spelt out in the columns next to it.

Resolution & payout

Polymarket-based markets settle through the UMA Optimistic Oracle on Polygon. A proposer submits the outcome, a two-hour challenge window opens, and unchallenged proposals finalise the resolution. Payouts settle automatically in USDC the moment the result is final — no bookmaker, no delay.

Kalshi-based markets settle in USD via the CFTC-regulated clearinghouse. Betfair Exchange settles in GBP/EUR net of commission. Manifold is play-money and does not pay out real funds.

UK Frequently Asked Questions

Is this market available outside the US?

Polymarket itself is geo-blocked in the US/UK/EU. Always check the legal status of prediction markets in your jurisdiction before trading.

What's the difference between YES and NO shares?

A YES share pays $1.00 if the event happens, $0 otherwise. A NO share pays $1.00 if the event doesn't happen. The market price between 0¢ and 100¢ is the implied probability.

Is Polymarket legal in the UK?

Polymarket is accessible to UK traders but is not UKGC-licensed. It operates under US CFTC jurisdiction. UK residents face no domestic legal prohibition on using it, but UKGC consumer protections do not apply. For UKGC-regulated alternatives, Betfair Exchange and Smarkets offer similar prediction-style markets.

Do I pay tax on prediction market profits in the UK?

UKGC-licensed platform profits (Betfair, Smarkets) are typically tax-free gambling winnings for UK individuals. Polymarket profits involve USDC crypto transactions, which HMRC treats as Capital Gains Tax events. Keep full transaction records and report via Self Assessment if gains exceed £3,000 per tax year.

How do I deposit on Polymarket from the UK?

UK traders typically fund Polymarket via Coinbase UK, Kraken or Revolut — buying USDC with GBP and transferring to a Polygon-compatible wallet (MetaMask, Coinbase Wallet). Polymarket's onboarding walks you through the bridging process. Typical GBP-to-USDC conversion costs 0.5–1%.